Murder case arrest: Stephanie Roof, 46 (pictured) was found fatally shot in her driveway in Pennsylvania in September 2016. Seven months later, police have arrested her neighbor, Josef Raszler

A Pennsylvania man has been charged with using a high-pressure air gun he had built himself to fatally shoot a neighbor with whom he had an affair more than a year prior.

Josef Raszler, 35, was brought up on charges of criminal homicide Wednesday in connection to the September 13 shooting of 46-year-old Stephanie Roof.

The mother-of-four was shot with a homemade metal projectile as she returned home that night and got out of her SUV in the driveway of her home across the street from Raszler's in Lower Macungie Township.

Police say Raszler acknowledged a romantic relationship with Roof that she ended in 2015, angering him.

Lehigh County District Attorney Jim Martin says investigators haven't found the weapon Raszler allegedly used, but they have evidence he researched making it and practiced with it at his parents' lake house days before Roof's killing.

The case began unfolding at 1am on September 13, 2016, when police got a 911 call about a shooting and responded to 6400 block of Pinecrest Lane to find Stephanie Roof lying in the driveway of her home.

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Crime scene: The mother-of-four was found shot in the chest in the driveway of her home in the 6400 block of Pinecrest Lane in Lower Macungie Township

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Raszler, 35, lived across the way from Roof in this home. Police would later find copper pipes, air tanks and an air gun trigger there

A search of Josef Raszler's home yielded numerous tools, including copper pipes and rifling markings, air tanks, and an air gun trigger, as well as melted lead.

When homicide investigators dug into Raszler's computer history, they allegedly found that he had searched terms like 'high pressure air pumps for air rifles,' 'high pressure air pump gun' and ‘most powerful air rifle.'

Receipts found by police indicated that in the months leading up to Stephanie Roof's killing, Raszler had purchased high pressure air gauges, air tanks and other equipment.

Roof, a mother-of-four (pictured in an old family photo with two of her kids and their father), had broken up with Raszler in 2015, angering him

In the course of what has been described as a 'painstaking and time-consuming’ seven-month investigation, detectives learned that on September 9 and 10, Raszler stayed at his parents' lake house in Schuylkill County, where neighbors later reported hearing sounds reminiscent of a pneumatic air gun going off.

Police also found two homemade metal projectiles and a target practice area.

While the actual murder weapon was never recovered, detective Mark Garrett, commander of the Lehigh County Firearm and Tool Mark Laboratory, was able to create an air gun from materials similar to those found in Josef Raszler's home using directions found online.

Stephanie Roof’s eldest daughter, Tricia Vanderford, told police that her mother had broken up with Raszler in April 2015 after four months but he refused to accept it and had ‘become obsessed’ with her, reported The Morning Call.

According to Vanderford, her mother was afraid of Raszler and kept her old cellphone that contained nearly 3,400 text messages from her jilted paramour filled with professions of love and declarations of hate.

Josef Raszler was arraigned on the homicide charges Wednesday and ordered held in the Lehigh County Jail without bail.